1. Field of the Invention
The present invention relates to a positioning device, a positioning method and a storage medium storing a program for determining position data of a plurality of points on a movement route.
2. Description of Related Art
A positioning device having an autonomous navigation function has been hitherto known. According to the autonomous navigation function, for example, after a reference point is measured by using a measuring unit which can measure an absolute position such as GPS (Global Positioning System), a moving direction and a moving amount are measured by using autonomous navigation sensors such as an acceleration sensor, an azimuth sensor, etc., and also displacement data obtained by the autonomous navigation sensors is being accumulatively added to the position data of the reference point, thereby calculating the position data of each point on a movement route.
Some correction techniques have been proposed for positioning devices having an autonomous navigation function (for example, JP-A-2008-232771, JP-A-11-230772). According to these correction techniques, when the calculation of position data based on the autonomous navigation function and the positioning based on GPS are simultaneously executed in the positioning device having the autonomous navigation function, the position data of that point is corrected on the basis of the positioning result of GPS and also measurement errors of the autonomous navigation sensors are corrected on the basis of the positioning result of GPS.
In general, when the calculation of the position data of the autonomous navigation function is continued, the error of the azimuth measurement and the error of the moving amount are accumulated, so that the error of the position data gradually increases. Particularly when the autonomous navigation function is added to a portable positioning device, a sensor for detecting an accurate speed such as a vehicle wheel speed sensor or the like cannot be provided, and thus the measurement error of the moving amount is also relatively larger.
However, the conventional technique in which GPS measurement is executed at a desired point while continuing the calculation of the position data based on the autonomous navigation function and the position data of the point which is subjected to GPS measurement is corrected has a problem that error accumulation increases in a section which is not subjected to GPS measurement, particularly at the rear end side of the section.
In the above correction technique, at each of points which are intermittently subjected to GPS measurement, errors which have been accumulated for the front stage of the point concerned is collectively corrected. Therefore, when a moving locus is represented by a series of position data, the difference in the position data between points before and after an error-corrected point is increased, and thus this correction technique has a problem that a continuous moving locus cannot be obtained.